Air intake silencer

ABSTRACT

An air intake silencer that can be quickly attached to the carburetor of a snowmobile&#39;&#39;s internal combustion engine. The silencer contains a tuning chamber which is sized for a given engine speed in order to reflect pressure waves to provide the greatest engine torque output. The air intake silencer also contains a silencing chamber which silences the audible sound waves which are emitted from the engine. A third chamber acts as a balancing chamber between the first two chambers to further improve the engine performance.

Jan. 23, 1973 United States Patent 1 Swanson et al.

FOREIGN PATENTS OR APPLICATIONS [54] AIR INTAKE SILENCER mmm m m &BB ccaa aaee rr FFGG 3987 5545 9999 956 Canada.......................,......

lllll [22] Filed: Nov. 26, 1971 Primary Examiner-Robert S. Ward, .Ir.Attorney-Alan G. Carlson et a1.

[21] Appl. No.: 202,357

[57] ABSTRACT An air intake silencer that can be the carburetor of asnowmobile [52] 11.8. Cl...............l81/35 A, 181/33 D, 181/33 E,

181/33 L, 181/59 .F0ln 1/02, FOln 1/06, FOln 1/08 Field of Searchquickly attached to 5 internal combustion [51] Int. [58] 181/33 D,3313,33 F, 33 H,

engine. The silencer contains a tuning chamber which 181/33 HA, 33 L, 35R, 35 A, 40, 48, 59 is sized for a given engine speed in order toreflect m n k md ea .m m

pressure waves to provide the greatest en References Clted output. Theair intake silencer also conta UNITED STATES PATENTS ing chamber whichsilences the audible sound waves which are emitted from the engine. Athird chamber 0. e me n a m fir. em r e S e C I mm w. 8. ma b ml i a w ea V r. mm p3 .m s, g m m C nnC that, e m m 63 ch ac RAAA 5555 3333 888002,869,670 2,954,096 McMullen Everett Addie et al.

AIR INTAKE SILENCER BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to noise silencers forinternal combustion engines and more specifically concerns air intakesilencers for use with snowmobiles which muffle noises escaping from theair intake system and which also improve the engines performance.

2. Description of the Prior Art The design and manufacture ofsnowmobiles is attended by a number of problems. Among these is thekeeping of the number of necessary components to a minimum to enablecompetitive manufacture while still providing a structurally sound,relatively noiseless pleasure vehicle. Of extreme importance is thenecessity of attenuating a significant portion of the sound generated bythe generally noisy two-stroke cycle engine which snowmobiles utilize.The prior art has dealt with this problem by muffling the exhaustsystem. However, in

, addition to muffling the exhaust path, a silencer should be providedin the air intake path to muffle noises escaping therethrough.

SUMMARY OF THE INVENTION The present invention pertains to an air intakesilencer for an internal combustion engine. The silencer provides a pathfor air to be supplied to the engine while it muffles noises escapingfrom the engine through the air intake system. The silencer containsthree chambers which act to destruct the pressure waves generated by theengine which cause audible noise and which tend to reduce engineperformance. The first chamber is a tuning chamber which is sized so asto change the phase of those pressure waves which are reflected backtoward the engine. This reflected wave destructively interferes withpressure wavesleaving the engine and properly calibrated increasesengine performance. The second chamber acts as a noise silencing chamberand it has a perforated tube through the center thereof, whichcombination has the effect of changing the phase of sound pressure wavesproviding for their destructive interference with other sound waves. Thethird chamber is a balancing chamber of the first two chambers whichfurther changes the phase of pressure waves thus further effecting theengine performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 isa side elevation view of asnowmobile having the air intake silencer mounted thereon; FIG. 2 is aview taken along line 2.2 of FIG. 1 showing the internal portions of theair-intake silencer; and

FIG. 3 is a view takenalong line 33 of.FlG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Drive sprocket 19 is driven by atwo-stroke cycle engine 25 which is mounted in an engine compartmentwithin engine-hood 27. For the supply of an air-fuel mixture to theengine crankcase a carburetor 29 is provided. Air intake silencer 31 isshown attached to carburetor 29 by apparatus which will be describedlater.

Referring now to FIGS. 2 and 3, the air intake silencer 31 is shown ingreater detail. Silencer 31 can be built from polyethylene or any othersuitable material. The silencer 31 is generally encased by front wall33, back wall 35 and side walls 37. These walls further define a topportion 39 and a bottom portion 41. A

bell-shaped air inlet port 43 is provided near the bottom portion 41 ofair intake silencer 31 to allow air to flow through the air intakesilencer 31 and out an air outlet port 45 to the carburetor 29.

In order to provide structural support and to dampen out shell noise inthe polyethylene air silencer 31, a rigid backing plate 47 is attachableto the silencer 31. Backing plate 47 has mounting holes (not shown) formounting to the silencer 31 and additionally has an air outlet opening51 and carburetor adapting holes 53. Bolts 55 are insertable throughholes 56 in walls 33 and 35 and through the holes (not shown) in backingplate 47 and held therein by nuts 57.

An adapter, generally designated 59, is provided to adapt silencer 31 tocarburetor 29. Adapter 59 has a front portion 61, a back portion 63, andstructural members 65. The distance between front portion 61 and backportion 63 is shorter than the distance between wall 33 and wall 35 inorder that when bolts 67 are inserted through holes 69 in front portion61, through holes 71 in back portion 63, through holes 53 in backingplate 47, and screwed within carburetor 29,

the walls will be compressed toward each other which abutting baffleplate-75 and top portion 39. Baffle plates 81 and 83 additionally have ahole 85 located therein.

Extending through hole 87 in baffle plate 75 and rigidly mountedthereto, and through hole 87 in baffle plate 77, and rigidly mountedthereto, is a perforated tube 91. Tube 91 is generally axial (along line3-3) with respect to air intake silencer 31 and has a portion 93extending past baffle plate 77 with a gradually increasing diameter.

A tuning chamber 95 is shown in the top portion of air silencer 31 andis generally defined by baffle plate 75, walls 33 and 35 and top portion39. A second chamber 97 acts as a'silencing chamber. and is generallydefined by baffle plate 75, baffle plate 77, walls 33 and 35, and sidewalls 37. A third chamber 99 acts as a balancing chamber and isgenerally defined by baffle plat. 77, walls 33 and 35, and bottomportion 41. As shown, balancing chamber 99 is open to the air by way ofbell-shaped air intake port 43, and tuning chamber 95 is open tocarburetor 29 through opening 15.

In the operation of snowmobile two-stroke cycle engines an air-fuelmixture is transferred from the carburetor to the'engine crankcasethrough an air intake port. This mixture is then transported to theengine crankcase tends to be extremelynoisy in-two-cycle en- -1 ginesThistnloise is.detected by the human ear since pressurewaves lof variousamplitudes and frequencies emanate from the engine through the exhaustsystem and additionally through theair intake system. It is a purpose ofthe present invention to silence these noices which escape through theair intake systemsThesiiencing is accomplishedvby the silencer chamberwith the perforated tube 91 therein. This combination acts essentiallyas a Helmholtz resonator to destroy a certain band of frequencies.Although the mechanics of the resonator are well known in the art, ingeneral, the combination has the effect of changing the phase ofpressure waves within the chamber in order that they can destructivelyinterfere with other pressure waves to reduce the amplitude of theresultant pressure wave and thus attenuate the audible noise. Withtwo-stroke cycle engines, we attenuate the low amplitude (0.00] psi)high frequency IUD- 10,000 cps) audible pressure waves.

Additionally, the present invention deals with the power loss which isassociated with silencing. Power output from the two-stroke cycle enginedepends principally upon having an air-fuel mixture which is under highcrankcase pressure in order to flow to the cylinder and to push theburned gases out of the cylinder exhaust port. However, with the pistonreciprocating within the cylinder at rapid speeds, high-amplitude(higher than approximately 0.001 psi), low-frequency waves (-300 cps)are generated from the crankcase and through the air intake system. Ifthe pressure within the crankcase is low at the closing of'the airintake port, the power output will consequently also be low. Whenproviding a restriction in the air intake path in order to silence thehigh-frequency, low-amplitude audible waves, the restriction may'reflectback toward the engine crankcase a higher amplitude, low-frequencypresthe crankcase and thus further reduce the crankcase pressure at airintake port closing. We found that this destructive interference doesoccur. Thus, in order to wavesback through the air intake system,- andto the crankcase, which are of different phase than pressure wavesemanating'therefrorn' in order to cause their destructive interference.A, pressure-time history is desired which provides peak pressure atairintakeclos I ing. Foran engine ata selected typical speed, theoptimal volume andshape of the tuning chamber 95 can bedete'rrhinedempirically by measuring engine torque output. The actual wavereflection is accomplished by the volume defin edrby top; portion 39,baffle-plates 81 and 83, walls and J5, and ,baffle plate ,75. The volumeoutside of baffle plates 81 and 83, offers very little additional tuningbut .is provided tomake silencer 31 more structurally sound andasthetically pleasing.

We found that the silencing chamber 97 tends to destroy the performanceof tuning chamber 95 since silencing chamber 97 reflects somehigh-amplitude, low-frequency waves which are in phase with the wavesemitting from the engine. In order to correct this, balancing" chamber99is providedfor further increasing the engine performance. Balancingchamber 99 reflects waves back through the air intake system whicharrive in chamber 99 at a later time than at'tuning chamber 95 and whenreflect ed are further out of phase than waves reflected from 'tuningchamber 95. These waves destructively interfere with waves emitting fromthe crankcase and with waves reflected by silencing chamber 97 in orderto increase crankcase pressure at air intake port closing thusincreasing engine performance. We found that by protruding tube 93 intobalancing chamber 99 and by providing an increasing diameter on tube 93,waves are gathered easisure wave which is in phase with pressure wavesleaving er which further increases engine performance.

What is claimed is:

1. For a snowmobile having a two-stroke cycle engine and a carburetorfor supplying an air-fuel mixture thereto, an air intake silencer,comprising: 7

a. a housing having a plurality ofchambers therein;

b. an air'intake port mounted on said housing for the transfer of airtosaid housing; v

c. an air outlet port for the transfer of air out of said d meansattaching said housing to said carburetor for the transfer of air fromsaid outlet port to said ,carburetor;

e. a tuning chamber defined by said housing for the reflection ofpressure waves of different phase from pressure waves emanating fromsaid twostroke cycle engine through said air outlet port;

' f. a balancing chamber definedby said housing and disposed therein sothat pressure waves emanating from said engine'reach said balancingchamber at v .a later timeth'an when said pressure waves reach saidtuning chamber for the reflection'of pressure waves of different phasethan said waves reflected from said tuning chamber and different inphase frorn said waves emanating from said two-stroke 2 An air intakesilencer for internal combustion engines, comprising:

a. ahousing; r b. an air intake port'mounted on said housing for thetransfer of air through said housing; c. an air outlet port for thetransfer of air out of said housing;

tive interference with other sound pressure waves.

d. first means disposed within said housing for changing the phase ofsound pressure waves providing for their destructive interference withother sound pressure waves;

e. second means disposed within said housing for the reflection ofpressure waves of different phase from pressure waves emanating fromsaid internal combustion engine through said air outlet port;

and

f. third means disposed within said housing for the reflection ofpressure waves of different phase than said pressure waves reflected bysaid second means, different in phase from any pressure waves reflectedby said first means, and different in phase from pressure wavesemanating from said internal combustion engine.

3. The apparatus of claim 2, wherein:

a. said second means includes a tuning chamber defined by said housing;I

b. said third means includes a balancing chamber defined by saidhousing; and

c. said first means includes a silencing chamber defined by said housingwith a perforated tube mounted therein with one end extending into saidtuning chamber and the other end having a gradually increasing diameterand vextending into said silencing chamber.

4. An air intake silencer for internal combustion engines, comprising:

a. a casing having walls, a top portion, a bottom portion, and an airinlet port for receiving air into said silencer and an air outlet portfor the transfer of air out of said silencer;

. first and second baffle plates mounted within said casing, said baffleplates having their peripheral edges secured to the interior of saidwalls and being spaced from each other and from the top and bottomportions of said casing, said first baffle plate associating with saidtop portion and said walls to define a tuning chamber, said outlet portopening said tuning chamber for the transfer of air out of saidsilencer, said first baffle plate and said second baffle plateassociating with said walls to define a silencing chamber, said secondbaffle plate associating with said bottom portion and with said walls todefine a balancing chamber, said inlet port connecting said balancingchamber to a source of air, each of said baffle plates having an openingtherein; and

a tube having a top end and a bottom end, said tube being mounted insaid opening in said top baffle plate and in said opening in said bottombaffle plate, said top end thereof extending into said tuning chamber,and said bottom end thereof extending into said balancing chamber, saidtube having a gradually increasing diameter at the bottom end thereofextending into said balancing chamber, said tube having perforations inthe walls thereof communicating with said silencing chamber.

1. For a snowmobile having a two-stroke cycle engine and a carburetorfor supplying an air-fuel mixture thereto, an air intake silencer,comprising: a. a housing having a plurality of chambers therein; b. anair intake port mounted on said housing for the transfer of air to saidhousing; c. an air outlet port for the transfer of air out of saidhousing; d. means attaching said housing to said carburetor for thetransfer of air from said outlet port to said carburetor; e. a tuningchamber defined by said housing for the reflection of pressure waves ofdifferent phase from pressure waves emanating from said two-stroke cycleengine through said air outlet port; f. a balancing chamber defined bysaid housing and disposed therein so that pressure waves emanating fromsaid engine reach said balancing chamber at a later time than when saidpressure waves reach said tuning chamber for the reflection of pressurewaves of different phase than said waves reflected from said tuningchamber and different in phase from said waves emanating from saidtwo-stroke cycle engine; and g. a silencing chamber defined by saidhousing and disposed therein so that pressure waves emanating from saidengine reach said silencing chamber at a later time than when saidpressure waves reach said tuning chamber and prior to when said pressurewaves reach said balancing chamber, said silencing chamber having aperforated tube mounted therein with one end extending into said tuningchamber and the other end having a gradually increasing diameter andextending into said balancing chamber for changing the phase of soundpressure waves providing for their destructive interference with othersound pressure waves.
 2. An air intake silencer for internal combustionengines, comprising: a. a housing; b. an air intake port mounted on saidhousing for the transfer of air through said housing; c. an air outletport for the transfer of air out of said housing; d. first meansdisposed within said housing for changing the phase of sound pressurewaves providing for their destructive interference with other soundpressure waves; e. second means disposed within said housing for thereflection of pressure waves of different phase from pressure wavesemanating from said internal combustion engine through said air outletport; and f. third means disposed within said housing for the reflectionof pressure waves of different phase than said pressure waves reflectedby said second means, different in phase from any pressure wavesreflected by said first means, and different in phase from pressurewaves emanating from said internal combustion engine.
 3. The apparatusof claim 2, wherein: a. said second means includes a tuning chamberdefined by said housing; b. said third means includes a balancingchamber defined by said housing; and c. said first means includes asilencing chamber defined by said housing with a perforated tube mountedtherein with one end extending into said tuning chamber and the otherend having a gradually increasing diameter and extending into saidsilencing chamber.
 4. An air intake silencer for internal combustionengines, comprising: a. a casing having walls, a top portion, a bottomportion, and an air inlet port for receiving air into said silencer andan air outlet port for the transfer of air out of said silencer; b.first and second baffle plates mounted within said casing, said baffleplates having their peripheral edges secured to the interior of saidwalls and being spaced from each other and from the top and bottomportions of said casing, said first baffle plate associating with saidtop portion and said walls to define a tuning chamber, said outlet portopening said tuning chamber for the transfer of air out oF saidsilencer, said first baffle plate and said second baffle plateassociating with said walls to define a silencing chamber, said secondbaffle plate associating with said bottom portion and with said walls todefine a balancing chamber, said inlet port connecting said balancingchamber to a source of air, each of said baffle plates having an openingtherein; and c. a tube having a top end and a bottom end, said tubebeing mounted in said opening in said top baffle plate and in saidopening in said bottom baffle plate, said top end thereof extending intosaid tuning chamber, and said bottom end thereof extending into saidbalancing chamber, said tube having a gradually increasing diameter atthe bottom end thereof extending into said balancing chamber, said tubehaving perforations in the walls thereof communicating with saidsilencing chamber.